Differentiation of targets in optical station based on the strength of the reflected signal

• US 6,400,447 B1
• Filed: 03/11/2000
• Issued: 06/04/2002
• Est. Priority Date: 03/11/2000
• Status: Expired due to Term

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Kirk, Geoffrey R, Lamm, Robert J.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Andrea, Brian K.
• Application Number:
  US09/524,426
• Time in Patent Office: 815 Days
• Field of Search: 356/4.07, 382/103, 382/181
• US Class Current: 356/4.07
• CPC Class Codes: G01C 1/02 Theodolites
• CPC Class Codes: G01C 15/002 Active optical surveying means optical plumbing G01C15/105
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: G01S 7/4802 using analysis of echo signal for target characterisation; Target signature; Target cross-section

Abstract

A system and method for selecting at least one target with strong reflectivity from a set of strong and weak reflectors by using an amplitude of a reflected signal to make such a selection. The pre-computed look-up table that relates an amplitude of the reflected signal from a target with a strong reflectivity to the distance at which such target is located is used in a real-time mode to separate weak reflectors from strong reflectors. In the post-processing mode the usage of normalizing function allows to further differentiate between strong reflectors (like windows) and very strong reflectors (like prisms).

Claims

1. A method of selecting at least one cooperative target from a set of targets, wherein said set of targets includes a subset of cooperative targets and a subset of non-cooperative targets;

said method comprising the steps of;

generating an optical signal by using an Optical Station;

directing said optical signal at each said target from said set of targets;

receiving at least one reflected optical signal by said Optical Station;

wherein each said reflected optical signal is reflected from one said target from said set of targets; and

wherein each said target is marked by said reflection;

matching each said reflected optical signal with one said target from said set of targets;

creating a database comprising a set of elements, wherein each element of said database includes a distance from said Optical Station to one said target from said set of targets and an amplitude of an actual signal reflected from said one target;

post processing said database to create at least one color, wherein each said color is a function of one said element of said database; and

creating a color-image of each said target using said at least one color corresponding to said target;

wherein said cooperative target has a substantially strong reflectivity in a direction back to said Optical Station;

and wherein said non-cooperative target has a substantially weak reflectivity in a direction back to said Optical Station.

2. The method of claim 1, wherein said step of creating said color-image of each said target further includes the steps of:

multiplying an actual amplitude of said signal reflected from said target by a normalizing function;

wherein said normalizing function creates a super-color for each said target; and

wherein said super-color is a function of said normalized amplitude of said actual signal reflected from said target; and

wherein said super-color for each said target does not depend on a distance of said target from said Optical Station; and

creating a super-color image of each said target.

3. A method of selecting at least one cooperative target from a set of targets, wherein said set of targets includes a subset of cooperative targets and a subset of non-cooperative targets;

said method comprising the steps of;

generating an optical signal by using an Optical Station;

directing said optical signal at each said target from said set of targets;

receiving at least one reflected optical signal by said Optical Station;

wherein each said reflected optical signal is reflected from one said target from said set of targets; and

wherein each said target is marked by said reflection;

matching each said reflected optical signal with one said target from said set of targets;

measuring a distance from said Optical station to each said marked by said reflection target from said set of targets;

generating a pulse train of signals related to a position of an encoder; and

correlating said pulse train of signals with said amplitude of said one reflected signal;

wherein said Optical Station includes an optical attenuator including a wheel, and wherein said optical attenuator is placed in the path of said reflected signal;

and wherein said wheel of said optical attenuator further includes said optical encoder.

4. A system for selecting at least one target from a set of targets comprising:

a means for generating an optical signal;

a means for directing said optical signal at each said target;

a means for receiving at least one reflected optical signal;

wherein each said reflected optical signal is reflected by one said target marked by said reflection;

a means for matching each said reflected optical signal to one said marked by said reflection target;

a database comprising at least one element, wherein each said element of said database further includes a distance from said Optical Station to one said target from and an amplitude of an actual signal reflected from said one target;

a means for post processing said database to create at least one color, wherein each said color is a function of one said element of said database;

a means for multiplying an actual amplitude of said signal reflected from said target by a normalizing function;

wherein said normalizing function creates a super-color for each said target; and

wherein said super-color is a function of said normalized amplitude of said actual signal reflected from said target; and

wherein said super-color for each said target does not depend on a distance of said target from said Optical Station; and

a means for creating a super-color image of each said target.

5. A system for selecting at least one target from a set of targets comprising:

a means for generating an optical signal;

a means for directing said optical signal at each said target;

a means for receiving at least one reflected optical signal;

wherein each said reflected optical signal is reflected by one said target marked by said reflection;

a means for matching each said reflected optical signal to one said marked by said reflection target;

a means for analyzing said at least one reflected signal in order to select at least one target from said set of targets;

a means for measuring a distance to each said target from said means for generating said optical signal;

a means for measuring an amplitude of each said reflected signal; and

a means for measuring a position of a wheel of an optical attenuator;

wherein said optical attenuator includes said wheel;

wherein said wheel of said optical attenuator further includes said optical encoder; and

wherein said optical attenuator is placed in the path of said reflected signal;

wherein said means for measuring said position of said wheel of said optical attenuator further includes;

a means for generating a pulse train of signals related to a position of an encoder; and

a means for correlating said pulse train of signals with said amplitude of said one reflected signal.